Heater panel



P. GALLEZ HEATER PANEL Filed April 16, 1964 April 11, 1967 FIG! 7 4 mmAA \\\v /V//// O G II A 2 F above disadvantages and also to advantageswhichwill be described hereinafter.

United States Patent 43,65 4 Claims. Cl. 219-522 This invention relatesto a heater panel comprising at least one plate of an electricallyinsulating material, the surface of which has two distributingelectrodes connected to an electrical power source, and an electricallyconductive film extending between the electrodes.

Heater panels of this kind are generally constituted of a sheet ofglass, one surface of which is covered with a thin film of metal or aconductive oxide, such as tin oxide. This film is used as aheater-resistance and is adapted to receive electrical power from anadequate source. To ensure that the electrical current is satisfactorilydistributed over the entire panel surface, two electrodes ofelectrically conductive material are disposed in two marginal zones ofthe film. Each of these strips is connected to one terminal of theelectrical power supply and forms a distributing electrode.

Heater panels of the above type maybe used as heating units forbuildings. They can also be used as transparent elements, particularlyfor motor vehicle Windshields.

It has been found that the temperature of operation of.

such panels varies substantially from one zone of their surface toanother. The temperature differences are due particularly to a lack ofuniformity in the electrical resistance of the conductive filrn. Despitethe care taken during manufacture, the layer of metal or metallic oxidehas a lower electrical resistance in certain zones, which for example iscaused by a local excess thickness. In these zones the current densityis increased to the detriment of the adjacent zones and hence thetemperature in such zones of greater current density is greater. Suchlocal overheating is damaging to the conductive film and to theinsulating sheet, which is also subject to damage.

It has also been found that there is frequently an irregular temperaturedistribution along the distributing electrodes because of variations inthe contact resistance between the electrode and the conductive film.Contact breaks may take place at the hottest points. They have theeffect of increasing the current density in the adjacent contact zonesand hence causing new breaks thereat.

It is an object of the present invention to eliminate the provide anumber of According to the invention, the conductive film is divided upinto a plurality of strips, each of which is in electrical contact witheach electrode.

- Although the strips receive electrical power from the same twoelectrodes, it will be seen that the current passing through each ofthem is determined by its own electrical characteristics. Since eachstrip is of a more uniform electrical resistance than the complete film,the current density is distributed therein more uniformly as well.

Advantageously, the strips forming the conductive film each have thesame Width measured along a line perpendicular to the direction of flowof the electric current. Preferably, each electrode has a contactsurface of the same area with each of the conductive film strips. Thestrips of the same width 'have the same electrical resistance if theirlength and their thickness are substantially the same which is mostfrequently the case. It is therefore advantageous to provide all thestrips with contact surfaces of the same dimensions with the electrodes.Preferably, each strip of the conductive film has separate contactsurfaces with each of the electrodes having areas which are in the sameratio as that of the total areas of the electrodes one to the other.This is particularly advantageous in the frequent cases in which the twoelectrodes are not of the same length, because the panel 'has anasymmetrical shape. This arrangement avoids an excessive current densityat the contact between certain strips and an electrode.

In certain advantageous embodiments of a panel according to theinvention, at least one of the strips of the conductive film has a localcontraction. The contracted zone is thus given a higher operatingtemperature than that of the other parts of the panel. In fact in thiszone there is a greater current density which evolves more heat. Thislocal overheating has none of the disadvantages which were mentionedhereinfore, because it can be adjusted exactly both as regards positionand strength. On the other hand, this embodiment is very advantageouswhen it is required to produce an intensive heat effect in one region ofthe panel. By way of example, the zone of a windshield situated in thepath of vision of the driver is advantageously heated fairly strongly inorder to eliminate more intensively any frost or mist tending to formthere.

The accompanying drawings illustrate several embodiments of theinvention and its advantages.

FIGURE 1 is an elevation of a windshield according to the invention.

FIGURE 2 is a section of the line IIII in FIGURE 1 to a larger scale.

FIGURE 3 is an elevation of another embodiment of a windshield accordingto the invention.

FIGURE 4 is a partial view of another form of windshield.

In the various figures like reference numerals denote like parts.

With reference to FIGURES 1 and 2, the windshield comprises a sheet ofglass 1 covered with a thin transparent film '2 of an electricallyconductive metal, such as, for example, copper. Distributing electrodes3 and 4 are provided in marginal zones of the film 2. Said electrodesare, for example, in the form or an electrically conductive enamel.Leads 5, 6 are connected to an electrical power supply (not shown) andare soldered to respective electrodes. Another sheet of glass 7 ismaintained on the film 2 and the electrodes 3 and 4 by a layer oftransparent adhesive 8. I

According to the invention the film 2 is divided into strips, e.g., 9,10 and 11. Each strip is in contact with the electrodes 3 and 4. Thestrips are formed by de positing the film 2 on the surface of the sheet1, then applying the electrodes 3 and 4 thereon in the form of aconductive enamel, and finally by forming grooves, e.g., 12, 13 and 14,by scoring the film 2 with a pointed tool. The grooves 12, 13 and 14extend through the entire thickness of the film 2 and isolate the filminto the distinct strips 9, 10, 11 etc. The width of the grooves may beas small as desired, because the adjacent strips are substantially atthe same electrical potential and are therefore effectively insulated bya fine groove.

In the arrangement illustrated, the strips 9, 10, 11 are of the samewidth. Each of these strips passes a current therethrough whoseintensity is determined by the electric resistance of the strip and bythe voltage of the supply. If unintentionally one of the strips, forexample 11, has zone 15 of greater thickness (shown in chain dottedlines in FIGURE 1), it has a lower electrical resistance and thereforepasses a current of slightly greater magnitude than the others. Sincethis current is distributed uniformly throughout the strip, the extraheat evolved is also spread over a large area. In contradistinction, ina continuous film, a zone such as 15 would 3 drain the current passingthrough adjacent zones of the film so that a considerable increase inthe current density would be developed in zone 'resulting in asubstantial increase intemperature. I In the windshield according to theinvention the draining ofthe current is prevented by the grooves 13 and14. Thus, random unpredictable heated zones caused by thicknessvariations will be localized by the individual strips according to theinvention.

The' windshield shown in FIGURE 3 has the form of an irregularquadrilateral. -The electrodes 3 and 4 are disposed parallel to oneanother and are each located near one side of the quadrilateral. To formthe strips 9, 10, 11, grooves are provided in the film 2 prior to theaffixing of the electrodes 3 and 4 so that the grooves extend beneaththe latter. i

The side zones16 and 17 of the film which are intended to receive theelectrodes 3 and 4 are of different lengths. They are divided into asmany zones of the same areae.g., 18' and 19 as there are strips 9,10,11, i.e., five in the example illustrated. Each electrode 3 or 4thereforehas contact surfaces of the same area with each stri-p 9, 10,11 etc. Similarly, each strip, e.g. 9, is in contact with the electrodes3 andv 4 at zones 18 and 19 whose areas are in the same ratio as that ofthe total areas of the side zone-s 16 and 17 of the electrodes 3 and 4one to the other.

The windshield illustrated in FIGURE 4 comprises the same elements asthe windshield shown in FIGURE 1. In addition, the transverse marginalzones 20 of the sheet 1 are covered 'by a layer of the same nature asthat used for the film 2. A groove 21 completely separates the zones 20from the film 2 and, on the one hand, from the adjacent strip 9 and, onthe other hand, from the electrodes 3 and 4. This arrangement isadvantageous in that the windshield is optically uniform. Moreover,since the zones 20 do not participate in conveying the electricalcurrent, the heat evolved is concentrated in the film 2, i.e.-,intheportion of the windshield which is most frequently looked through.

The'strip 10 shown in FIGURE 4 has a contracted zone 22 formedby causingthe grooves 12 and 13.t o converge towards one another in 'a centralzone of the sheet 1. To this end, each of'the latter grooves com-'prises two portions 23, 23 which converge in'the con tracted zone "22.Despite the presence'of the latter, the electrical resistance of thestrip 10'is" not very much different fromthat of the other strips'sothat the current intensity flowing through it is substantially the same.On the other hand, in the contracted'zone '22 the current density andthe electrical resistance are relatively high so that the heat evolvedthere is greater than in the other zones of the film 2. This arrangementis very advantageous in Windshields of motor vehicles, where. it

, enables mist and frost to be rapidly eliminated at certain selectedlocations, for example in front of the driver.

r The invention is not limited to the embodiments describedhereinbefore. Variations and modifications are possible, moreparticularly by combining the features of the embodiments illustrated.The invention may also be applied to panels used for heating buildings,

What I claim is:

4 ,1. .A. heater panel comprising at least one electrically insulatingglass sheet, an electrically conductive transparent film on said glasssheet, a single pair .of electrodes extendiig parallel to each other incontact with said film along the entire length of said film in marginalzones of said glass sheet, said electrodes being adapted for beingconnected to an electrical power source, said film having a plurality ofgrooves extending between the electrodes for isolating the film oneither side of the grooves to define a plurality of isolated stripsextending from one electrode to the other and in electrical contacttherewith, said glass sheet being of quadrilateral outline and saidgrooves converging in one direction.

2'. Aheater panel as claimed in claim 1 grooves extend along straightlines.

3. A heater panel comprising at least one electrically insulating glasssheet, an electrically conductive transparent film on said glass sheet,a single pair of electrodes extending parallel to each other in contactwith said film along the entire length of said film in marginal zonesofsaid glass sheet, said electrodes being adapted for being connected toan electrical power source, said film having a plurality of groovesextending between the electrodes for isolating the film on either sideof the grooves to define a plurality of isolated strips extending fromone electrode to the other and in electrical contact therewith, saidelectrodes having diiferent lengths and each strip wherein said of filmbeing in contact with each of the electrodes along separate contactsurfaces having areas which are in the same ratio as the ratio of thetotal areas of the electrodes one to the other.

4. A heater panel comprising at least one electrically insulating glasssheet, an electrically conductive transparent film on said glass sheet,a single pair of electrodes extending parallel to each other in contactwith said film along the entire length of said film inmarginal zones ofsaid glass sheet, said electrodes being adapted for being connected toan electrical power source, said film-having a plurality of groovesextending between the electrodes for isolating the film on either sideof the grooves to Y define a plurality of isolated strips extending fromone electrode to the other and in electrical contact therewith, saidparallel electrodes having different lengths and said strips having thesame width measured along any line parallel to the electrodes.

References Cited by the Examiner Schmidt 338-211 RICHARD M. WOOD,Primary Examiner.

Y. MAYEWSKY, Assist nt Examiner.

1. A HEATER PANEL COMPRISING AT LEAST ONE ELECTRICALLY INSULATING GLASSSHEET, AN ELECTRICALLY CONDUCTIVE TRANSPARENT FILM ON SAID GLASS SHEET,A SINGLE PAIR OF ELECTRODES EXTENDING PARALLEL TO EACH OTHER IN CONTACTWITH SAID FILM ALONG THE ENTIRE LENGTH OF SAID FILM IN MARGINAL ZONES OFSAID GLASS SHEET, SAID ELECTRODES BEING ADAPTED FOR BEING CONNECTED TOAN ELECTRICAL POWER SOURCE, SAID FILM HAVING A PLURALITY OF GROOVESEXTENDING BETWEEN THE ELECTRODES FOR ISOLATING THE FILM ON EITHER SIDEOF THE GROOVES TO DEFINE A PLURALITY OF ISOLATED STRIPS EXTENDING FROMONE ELECTRODE TO THE OTHER AND IN ELECTRICAL CONTACT THEREWITH, SAIDGLASS SHEET BEING OF QUADRILATERAL OUTLINE AND SAID GROOVES CONVERGINGIN ONE DIRECTION.